Vicky Evans, director, Twinfix Limited, discusses the comparison of polycarbonate and glass in overhead glazing.
Polycarbonate, a modern day engineering thermoplastic glazing sheet, offers many benefits over glass for use in overhead glazing.
Polycarbonate sheet, with its high strength to weight ratio, is very light in weight, but also highly resistant to shattering and breakage. This shatter resistance makes the material much safer to use than glass, especially in overhead applications such as those found in railway station canopies or factory and office roof lights.
The key benefit of using polycarbonate glazing is safety. There is very little risk of it breaking during transport, installation and in situ. It can also be installed within a panellised roof glazing system that has been classified as non-fragile to the HSE’s recommended drop test ACR001:2014.
Let’s take a closer look at some of its key advantages.
Solid polycarbonate has been used as vertical anti-vandal and security glazing for decades. Correctly fitted with a wide edge engagement it will withstand attack from a sledge hammer. Nowadays, both the solid and the multiwall products are also used for overhead glazing applications. Due to its virtually unbreakable characteristics, there is no danger of breakage during transit, installation and in situ, unlike glass. Installing polycarbonate can even result in cost savings as many contractors include an additional percentage in their quote to allow for glass breakage.
Using polycarbonate in overhead situations means no cracks, so no rain dripping in and no glass dust, fragments or shards falling onto people below.
In an effort to improve the safety of those working on roofs, the HSE recommends the use of non-fragile overhead glazing and has worked with the Advisory Committee for Roofwork to devise a suitable drop test to establish the fragility or non-fragility of roofing assemblies. CDM regulations advise that, wherever possible, risks should be designed out, so specifying non-fragile roof lights makes a great deal of sense all round and contributes to compliance with working at height regulations.
However, a note of caution here: do ensure that the products being fitted conform to the ACR test. Just using polycarbonate glazing will not comply – the complete roof light structure needs to pass the test. It’s wise to ask for test certification from your supplier.
Weight Six millimetre solid polycarbonate glazing weighs 7.2kg/m2, substantially less than the glass alternative – 7.5mm laminated glass weighs 15kg/m2, while 25mm multiwall weighs only 3.5 kg/ m2. The product’s light weight means it is physically easier to get it onto a roof and it doesn’t have to be installed with heavy steel bars as lighter aluminium glazing systems may be employed. Such systems also require little to no future maintenance.
Use of polycarbonate glazing can therefore offer a safer long- term solution for roof glazing due to reducing the strain imposed on a building’s structural steelwork. This can be a major consideration in refurbishment projects.
Unlike its glass counterpart, polycarbonate is virtually unbreakable, therefore no costly replacement of glazing is required in future, contributing to a lower whole life cost of the roof. It will withstand natural forces like severe wind, hail, and snow storms as well as absorbing any building movements caused by such weather. It retains it properties at both high and low tempera- tures, +100oC to -40 oC. This resistance to vibration damage makes it the ideal product for use where the roof also incorporates an overhead crane or in a railway station where trains are moving about underneath.
Choice of type, tint and finish
Nowadays you can choose from a wide range of different polycarbonate products, in a range of tints, depending upon your needs and where the product is going to be used. Solid polycarbonate provides a high level of security, while the multiwall version is incredibly light in weight yet acts like double glazing. There are alternative types of polycarbonate that look like traditional Georgian wired glass, but have the many benefits of 6mm solid polycarbonate, and are proving to be great successes in heritage areas.
We’ve already mentioned that polycarbonate is incredibly light in weight, and this offers environmental benefits as it requires less energy to be used during transportation and installation. If you combine multiwall glazing with a thermally broken glazing bar, you can achieve great U-values. As you can also recycle polycarbonate at the end of its long lifespan, overall it has good ‘green’ credentials.
Access panels can be fitted into some polycarbonate roof light systems, enabling regular maintenance tasks, such as gutter cleaning, to be undertaken while standing on scaffolding erected underneath the roof, rather than having to access the gutters from above, which, for safety reasons, most companies try to avoid wherever possible. This would be difficult to achieve with a glass system and would probably not be approved for use as it would prove challenging and dangerous to those trying to do it.
We believe the above demonstrates that the high-performance and sustainable benefits of polycarbonate are far superior to glass for many commercial and industrial overhead glazing applications.